It is highly likely the number of infections is underreported (especially in the USA) because of the CDC’s instructions on who should be tested:
https://www.cdc.gov/coronavirus/2019-ncov/lab/tool-virus-requests.html
Should I be testing all patients for COVID-19?
At this time, CDC only recommends diagnostic testing of patients who meet the clinical criteria for a COVID-19 person under investigation (PUI), per Interim Guidelines for Collecting, Handling and Testing Clinical Specimens from Persons Under Investigation (PUIs) for Coronavirus Disease 2019 (COVID-19).
People who have been in close contact with a confirmed COVID-19 patient, and people who live in or recently traveled from an area with sustained transmission, are at elevated risk of COVID-19.
For more information about interpreting test results, see section labeled “Interpretation of test results from CDC 2019 novel coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel.”